Field of Invention
The present invention relates to a flexible-die forming apparatus and method for sheet metal, and more particularly to a sheet flexible-die forming apparatus and method by using magnetorheological elastomer as a flexible-die.
Description of Related Arts
Rubber-forming (including polyurethane rubber forming) is a well-known and widely-utilized manufacturing method. Silicon rubber and polyurethane rubber have a number of superior mechanical properties such as large hardness range, high elasticity, or high material strength. These properties make them extremely suitable as a flexible-die for rubber-forming. Different compositions of raw material and manufacturing methods determine the ultimate quality of the resulting rubber. Among many material properties, elasticity modulus is a very important material property which affects the quality of resulting products.
Conventionally, in rubber-forming a manufacturer needs to, depending on the material property and shape characteristics of desirable products, select a kind of rubber which has the most suitable elasticity modulus as flexible-die. However, the deformation and stress states of sheet metal changes during the forming process. During initial forming stage, the rubber should possess a relatively higher elasticity modulus (i.e. generally harder) to provide larger force with the same deformation. During later stage, the rubber should possess a relatively lower elasticity modulus (i.e. generally softer). When the rubber is softer, it can flow easily into the cavity and ensure the sheet to achieve the desired shape, which is especially important for forming the products with small radius curved surface. Unfortunately, conventional rubber does not possess the above-mentioned property during a typical rubber-forming process. The elasticity modulus remains constant throughout the entire forming process. This disadvantage substantially hinders the development of rubber-forming. If, it is possible to alter the elasticity modulus of the rubber during a typical forming process, the sheet metal flow can be adjusted and optimized, and the formability of sheet metal and the quality of the products would be substantially improved.
New material developed in recent years provides a possibility for resolving the above-mentioned problem. Magnetorheological elastomer is a very promising smart material, which is a class of solids that consist of polymeric matrix with embedded micro-sized ferromagnetic particles. Because of this particular composite microstructure, the mechanical properties (such as elasticity modulus) of these materials can be altered by the application of magnetic field. This smart material is more controllable, having rapid response in changing mechanical properties, superior material stability during a typical forming process. The change in mechanical properties for this material is also reversible. Currently, many scholars are researching the applicability of magnetorheological elastomer in noise abatement and control of motor vehicles, trains and ships. Among all magnetorheological elastomers, magnetorheological elastomer with silicone rubber or polyurethane rubber as polymeric material have been widely utilized. The elasticity modulus of the magnetorheological elastomer by using silicone rubber or polyurethane rubber as polymeric material can be altered by adjusting the applied external magnetic field strength.